Mechanical and flame retardant properties of polylactide composites with hyperbranched polymers

Hyperbranched polymers (HBP6) with polyethylene glycol (PEG) chains were synthesized via bulk polymerization of diepoxide, primary amine, and monoepoxide. Polylactide (PLA) composites, with aluminum trihydroxide (ATH) and HBP6, were prepared via direct melt compounding using a brabender. The limiting oxygen index (LOI) could be raised to 44% for the PLA composite with 29 wt% ATH and 1% HBP6. A UL-94 V-0 rating could be achieved by adding ATH and HBP6 to the PLA matrix. The HBP6 has a lower glass transition temperature (Tg), approximately −31 °C, and its incorporation as a plasticizer could increase the impact strength of a PLA blend or composite. The elongation at break could be increased from 5% for neat PLA to 83% for the PLA composite with an addition of 10% of HBP6 and 20% ATH. The enhancement of impact strength of the composite was not only attributed to the decrease in Tg, but also the dispersion of second-phase HBP6 domains formed by the phase separation.